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Thread: Specific 7mgte Rebuild Tips

  1. #1
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    Default Specific 7mgte Rebuild Tips

    I would like to thank Tony Mawad for saving this info that took me a very long time to type out. Had he not saved it, it would have been lost when the site crashed in March of 2005.


    SPECIFIC 7MGTE REBUILD TIPS PART 1

    This is intended to serve as a guide and to share the lessons that I've learned through the thousands of dollars I've spent. If you plan on rebuilding your 7M, please consider what I have to say. This isn't an all-inclusive guide or "everything you need to know". This is only intended to be supplemental information. You still need to familiarize yourself with basic engine maintenance techniques available in any Haynes or Chilton's manual. See also http://www.cygnusx1.net/

    PAY ATTENTION!

    When selecting your machine shop, look at their operation. It would be in your best interests to select the machine shop that has the cleanest setup and the newest, most accurate equipment. Many machine shops cannot correctly machine components for our engines.

    The 7MGTE oil system is a high-flow, low-pressure system. At idle, the stock specification from toyota for oil pressure is 4.3psi. Yes, I said 4.3 psi, NOT 43 PSI! From the factory, the 7MGTE has rod clearances of .0008 to .0021, total thrust washer clearance of .002 to .009 (thats the clearances of both sides added together) and crank main bearing clearances of .0012 to .0019.

    Check your oil pump drive shaft clearances:
    http://www.cygnusx1.net/supra/libra...M/em/EM_84.html

    Also -ensure your camshafts have the correct clearance. .0014-.0028 for the number 1 and .0010-.0037 for the rest of the journals.

    Clearances too large will contribute to low oil pressure.

    In additon, you should keep in mind that with such tight clearances it is possible for the measurements to change significantly with a change in temperature. If you take home your crankshaft, pistons, etc and re-measure them in your 0 degree garage, the measurements will probably change from the climate controlled readings of the machine shop. (And vice versa) Keep everything the same temperature for the whole process.

    And, keep in mind that your mic might read different than your machinist - compare notes. Bring your mic in to check it out.

    Many machine shops feel that it is necessary to make the clearances larger on these motors for "high performance" applications because thats what they do for the V8's. This, quite simply, is not the case. I learned this when I lost my first motor. Clearances that are too large will lead to a significantly lower oil pressure at idle and take out your bearings.

    So, with that being said, BUILD THE ENGINE TIGHT. And always, I repeat always double check ALL measurements for yourself with a micrometer. Check your crankshaft, rods, piston bore, etc. etc. Dont trust the machinist to make sure that they are all correct. You will have a lot of time and money in this - dont let it go to waste.


    PISTON FITMENT TIPS

    Any reputable machine shop will wait until they have the pistons before they bore the block. If they want to bore the block before they have the pistons walk away with your engine because they are RETARDED!!

    If you coat the pistons with any type of thermal barrier, consider the fact that they might not expand as intended from the manufacturer. Add .001 of clearance if you moly-coated the skirts.

    HKS used to sell 85.5mm pistons - which are actually quite larger than the stock bore. I would limit any custom piston size to that.


    MACHINING AND PREPPING THE BLOCK

    Ensure that the rear timing cover is bolted to the block when you mill the top. If it isnt, your head will be held up by it and not seal correctly against the block surface.

    Ensure that your machine shop gets it smooth. The first block I had done still had pits in it. My machinist insisted it would be "fine". Fuck him. Ill talk more about surfacing for your head gasket later.

    A good machine shop will paint the block exterior, and ensure that all of the oil and coolant passages are clean upon the delivery of the block. If they are full of rust and debris when you blow out your oil passages before assembly, be sure to bring it up to your machinist.

    CLEAN OUT THAT ENGINE!!!! Keep it clean - your oil passages should be spotless before assembly. Get a drip pan under your engine block while it is on the stand and blow it out with WD-40, air, with a final rinse of engine oil. Remove the piston oil squirters and ensure that they arent stuck open for some unknown reason. Ensure that they are clean and move freely. They have a check valve in them that shouldnt allow oil past at lower psi. Once you get the block clean, reinstall and torque to specs.

    Check your oil filter housing. There are two relief valves in the housing - one bypasses oil to the oil cooler and the other bypasses oil in the event that the filter clogs. Ensure they are clean and installed in the correct DIRECTION.

    Tap out all of the bolt holes and follow up the tap with a gun bore brush. You will make things easier on yourself.
    And always, always cover it up when you're done for the day. Avoid dust-kicking drafts in your work area at all times. A trash bag with the little yellow handles that sinch it up works well.

    CLEAN YOUR CRANKSHAFT OIL PASSAGES - same as above. If your crankshaft has a groove worn in the ends from the oil seal, you can purchase a repair sleeve that will fit right over the end.


    ASSEMBLY OF YOUR SHORTBLOCK

    Measure and set your ring-end gaps.

    Use plenty of moly-based lube on your bearings during assembly.

    I dislike plastigauge, my personal belief is that a good set of mics are far more accurate. However, plastigauge can be a good indicator of where you stand with your clearances - just dont rely on it.

    Use ARP hardware - the new main stud kits have been changed. (The Supra community can thank me for that.) The old kits used to hit the pickup tube for the oil pump. Be wary if you have picked up an old kit.

    Get a quality torque wrench.

    PREPPING AND ASSEMBLING THE HEAD

    The first thing you should do, before doing ANYTHING to the head you plan on rebuilding, it have it inspected and cleaned by a competent machinist. But be wary! I once had a machinist bead blast my journal surfaces He thought that bearings were supposed to go in there.

  2. #2
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    Default Re: Specific 7mgte Rebuild Tips

    A mild street port will do the engine well. You dont have to go overboard and can finish the job in less than a week, part time. http://www.standardabrasives.com/ should give you a good tutorial on basic head porting. It really isnt that hard as long as you keep it simple and just gasket match the manifold to the head, smooth out the casting flash and the valve seat ridges. DO NOT PORT MATCH THE EXHAUST MANIFOLD TO THE HEAD. Opening up the exhaust ports on the head removes the reversion dam and will cause you to lose torque because the manifold will no longer scavenge the head. If you doubt me, search.

    Camshafts from the 7M will oftentimes have a gouged appearance to them. They are fine, and you will be hard pressed to find a set that arent the same way anywhere else. The "gouging" or "scoring" is caused by aluminum buildup from the head. Dont polish them unless they are extremely rough. Polishing the aluminum off will only make your clearances larger in the head and contribute to oil pressure loss. The aluminum will only build up again over time.

    In my opinion, aftermarket valvetrains with stronger springs are a waste of time. These engines werent made to rev anyway. A stock valve system is adequate, but gains can certainly be seen through larger valves. Ive heard of people fitting 2jz valves into these heads as a cheap solution - youll have to research that one on your own.

    Schneider racing cams does a good job at regrinds.

    Some people fit NA cams into the turbo block for gains on the bottom end. A dyno was floating around where somebody changed out one for the other and you can clearly see that NA cams peak at a lower rpm. Sure, this is great for under 350hp supras, but if you are going for big numbers with a big turbo keep the stock, turbo cams or order some performance regrinds from Schneider.

    Set the valve lash (+.002 over TSRM) at about .010 on the intake and .012 on the exhaust for initial break in. Valves tend to seat a little bit - this will give the valves room to seat without sticking open.

    You can get replacement valve shims from toyota for $$$$$$ or you can go to your local machine shop and get them $$. If your machine shop doesnt stock them look around more. I get mine from a machine shop for 3 bucks a piece.

    Check the exhaust manifold bolt holes and helicoil if necessary.


    SELECTING AND PREPPING FOR A METAL HEAD GASKET

    This topic has been beaten to death. Here is my opinion from my experience:

    Different head gaskets will yield different compression ratios from your engine. You need to consider all parameters when selecting a head gasket. Get an online compression calculator that considers engine bore, stroke, piston deck height, piston dish volume, head volume, head gasket thickness, head gasket bore. Yes, you actually need to measure these things. This is one of the most important things you will do. 1mm thickness change in a HG can change your compression dramatically. An 83mm bore hg compared to an 86mm bore hg can do the same thing. The bottom line is this: YOU NEED TO KNOW WHAT YOUR COMPRESSION RATIO WILL BE. Dont be a dumbass, figure it out so you wont run 20 psi on 9:1 when you think its 8.4:1. Also, you dont want to be stuck with a 7.5:1 slug that you thought had stock compression.

    You can re-use an HKS MHG. Just spray it thouroughly with that copper spray from napa. This will fill in the irregularities from a standard machining. It is not necessary to lap the head when you use this stuff.

    DO NOT USE IT IF YOU STILL HAVE THE LAYER OF RUBBER ON A BRAND NEW HKS MHG.

    HKS recommends an RA of something like 15? microns or less. Dont quote me on that exact figure but its close. No machine shop will be able to accomplish that without some really advanced equipment. IMO, a copper head gasket would work well, but I have yet to use one. Some people have used the permatex brake quiet instead of the copper spray. I know it sounds goofy, but supposedly it works.

    INSTALLING THE HEAD

    Use ARP studs. No, they dont clamp more than the bolts, they provide a more well-distributed torque. With bolts it is possible to read 80ft/lbs with a torque wrench and not have the appropriate clamping force because junk was in the threads of the block.

    You DID remember to machine the front timing cover with the block, RIGHT?


    LAST BUT NOT LEAST

    Do not break in an engine with synthetic oil. It is too slick. Manufacturers do not design their rings to be broken in on synthetic and they will not seat correctly. Use dino oil for the first 1000 miles. Change it after the first test drive, 50, 500, and to synthetic at 1000. (Just my method, do what you like) Drive it hard.


    Good luck.

  3. #3
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    Default Re: Specific 7mgte Rebuild Tips

    Nice post, and good tips.

    If you re-use any MHG, make sure you clean it first with brake cleaner. (Takes off all the hylomar/rubber etc.) Generally that stuff tends to degrade over time. My Greddy MHG did not have any from the start.

    I've found the Brake Quiet to be very effective on these bare gaskets to seal up all the smaller scratches and stuff. No leaks yet, and it's been done 4 times to this Greddy gasket.. still no leaks...

    Last time around, we did machine the right bore into the gasket by clamping it between the block and the tourqe plate. I can't say enough how important the tourqe plate proved to be. It changed the bore by 4k in places.. That is quite a bit, and would take alot of ring wear to seal up, if it would seal up at all.

    Nice write up 5150.

  4. #4
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    Default Re: Specific 7mgte Rebuild Tips

    reviving old thread!
    question about the freeze/expansion plugs. do they ever need to be replaced if you dont live anywhere close to freezing temps? doing a rebuild so i wanna do it right the first time around

  5. #5
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    Default Re: Specific 7mgte Rebuild Tips

    You don't HAVE to replace them. But it's easier to do while the engien is out already. Extreme PITA to do in the car depending on which one gives you issues (trust me, i went through it). They're really cheap so you might as well just replace them. Saves hassle later
    Boosted Pleasure

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    Default Re: Specific 7mgte Rebuild Tips

    Thank you for the great info.

  7. #7
    gilbertmk3
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    Default Re: Specific 7mgte Rebuild Tips

    Quote Originally Posted by p5150 View Post
    A mild street port will do the engine well. You dont have to go overboard and can finish the job in less than a week, part time. http://www.standardabrasives.com/ should give you a good tutorial on basic head porting. It really isnt that hard as long as you keep it simple and just gasket match the manifold to the head, smooth out the casting flash and the valve seat ridges. DO NOT PORT MATCH THE EXHAUST MANIFOLD TO THE HEAD. Opening up the exhaust ports on the head removes the reversion dam and will cause you to lose torque because the manifold will no longer scavenge the head. If you doubt me, search.
    serious?? i just opening a little bit .. and i polish

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